1. Field of the Invention
This invention relates generally to golf club head fabrication and more particularly to a method of forging a face for a golf club head and certain configurations of the face.
2. Description of Related Art
Three manufacturing methods are used to produce metal wood golf club heads. Such heads are generally hollow one piece assemblies made-up of a body sealed by a face which is used to strike the golf ball. The first, and most common method uses the metal casting process for the manufacture of the body with a cast or otherwise formed face. This method results in excellent shape for various designs and gives optimum weight distribution for wall thickness variation. However, casting porosity problems often present structural quality concerns particularly for the hitting face. The second method utilizes the common forming and assembling processes using plate and sheet stocks to achieve cost reduction. However, this approach imposes engineering-quality concerns from oxide contamination due to large weld regions, resulting in a tendency toward cracking due to inclusions of contamination and porosity on welding structures of several pieces. This process also suffers from structural discontinuities, non-homogenity, and problems related to dimensional stability and tolerances. The third method uses the forging process, which is capable of refining microstructure and properties from cast and from formed and welded products. It provides excellent product quality and performance, but this method is much more costly.
Manufacturing methods of these parts has evolved so that today most metal wood golf club heads are made with a cast body and forged face. This, apparently offers the most cost-effective manufacturing method, and gives excellent face design flexibility for higher performance. This process uses the casting process to produce a head body with a top or crown, bottom or sole plate and a neck or hostel portion. The forging process produces the hitting face. This has become a very common manufacturing method for producing titanium metal wood golf club heads. The cast-body with forged-face allows the head to be made from a wide range of materials and designs. It provides a high performance hitting face structure in an economic package. This approach avoids the defects often found in the other manufacturing approaches. However, the hitting faces produced by the forging or forming methods have not been optimized to produce superior products. This invention teaches a method for producing such products wherein the metallurgical capability in materials and in processing is able to further improve face performance and increase the degree of design freedom and product durability.
The following art defines the present state of this field:
Anderson, U.S. Pat. No. 5,024,437 describes a golf club head having a main body portion formed by investment casting of material such as stainless steel, beryllium copper, titanium, or aluminum. The face plate of the head is formed of a forged metal such as forged carbon steel, this plate being welded to the face portion of the casting to form an integral assembly therewith. The forged metal faceplate affords a more solid impact and feel to the club which provides better control.
Bhowal et al., U.S. Pat. No. 5,026,520 describes fine grain titanium forgings and a process for refining the grain size of alpha. and .alpha.-.beta. titanium alloys through forging and recrystallization above the alloy""s .beta.-transus temperature. Specifically, the method employs an isothermal press in which a billet heated above the alloy""s .beta.-transus temperature, forged to produce an elongated, flattened grain structure, is held above the alloy""s .beta.-transus temperature for a predetermined time to allow fine grains to nucleate and grow through recrystallization, and then is quenched to arrest grain growth and to establish a fine grained titanium alloy. A second forging step may be employed to attain an aspect ratio of the grains. The fine grained titanium forgings made by this process have a maximum prior .beta.-grain size of 0.5 mm throughout the workpiece.
Anderson et al., U.S. Pat. No. 5,094,383 describes a golf club head having a main body portion formed by an investment casting of material such as stainless steel, beryllium copper, titanium, and aluminum. The face plate of the head is formed of a forged metal, such as forged carbon steel, this plate being welded to the face portion of the casting to form an integral assembly therewith. The forged metal faceplate affords a more solid impact and feel to the club which provides better control. Also, it has very high strength. Preferably, the head consists of cast stainless steel, and the face plate of forged stainless steel, both steels being of the same composition.
Anderson, U.S. Pat. No. 5,261,663 describes a golf club head having a main body portion formed by an investment casting of material such as stainless steel, beryllium copper, titanium, and aluminum. The face plate of the head is formed of a forged metal, such as forged carbon steel, this plate being welded to the face portion of the casting to form an integral assembly therewith. The forged metal face plate affords a more solid impact and feel to the club which provides better control. Also, it has very high strength. Preferably, the head consists of cast stainless steel, and the face plate of forged stainless steel, both steels being of the same composition. Face plate metal is preferably re-distributed toward the toe and heel of the head.
Takeda, U.S. Pat. No. 5,460,371 describes a metallic golf club wood head comprising a substantially planar face member welded to a container-shaped rear shell member having an open front face. A shaft connecting portion 7a is forged integrally with an upper portion of the face member 11a. A cut-out 14a is formed in an upper face of a front side of a rear shell member 12a for accommodating a lower portion of the shaft connecting portion 7a. As a result of this construction the number of structural members is reduced and the strength of the shaft connecting portion 7a is increased. Furthermore, the loft angle can be adjusted when manufacturing the face member 11a for example by forging. Moreover, since it is sufficient for the shaft connecting portion 7a to be formed at the top of the head only, the front side of the head can be lightened and the xe2x80x9csweet areaxe2x80x9d increased.
Preiss, U.S. Pat. No. 5,848,648 describes an improved process for the preparation and fabrication of horseshoes whereby pure titanium or titanium alloys are processed with the exclusion of contaminating gases such as oxygen, nitrogen and hydrogen. The titanium horseshoes have many advantages over the present state of art such as light weight, higher tensile strength, flexibility, wearing resistance, abrasion resistance, hypoallergenic, workability, formability, friction-free, physiologically inert, and are easily formed and shaped into the desired configuration.
Coulon, U.S. Pat. No. 5,545,271 describes A semi-finished product is taken made of a metastable beta titanium alloy containing oxygen in the range 0.4% to 0.7% by weight, and nitrogen in the range 0.1% to 0.2% by weight (oxygen+nitrogen.ltoreq.0.8%). The product is subjected to solution treatment at a temperature in the range 800.degree. C. to 900.degree. C. It is then cooled very quickly (.gtoreq.200.degree. C. per hour), the part is machined, ageing treatment is applied at a temperature in the range 550.degree. C. to 650.degree. C. for in the range 10 minutes to 2 hours so as to transform half of the beta titanium into alpha prime titanium. The titanium alloy part contains 40% to 60% of beta alloy, the remainder being alpha prime alloy. The part has good mechanical properties, good breaking strength, and a good elastic limit.
Hancock et al., U.S. Pat. No. 6,089,070 describes an improved golf club head and an improved method of manufacturing of a golf club head. More particularly, the invention relates to an improved metal wood golf club head and improved method of manufacturing a metal wood golf club head. The invention provides a metal wood golf club head including a one piece precision hot forged body portion comprising a hosel, a sole and a hitting face. The invention also provides a method of manufacturing a metal wood golf club head including the step of integrally forming a body portion of the club head comprising a hosel, a sole and a hitting face. The body portion of the club head is made by precision hot forging a billet of material, particularly titanium or alloys thereof, or alternatively, aluminium or alloys thereof.
Takeda, U.S. Pat. No. 6,200,228 describes a golf club such as an iron golf club comprising a head body with a cavity formed on the rear surface thereof and a back member securely fitted into the cavity, with the both closely contacted each other. Prior to securing a back member 9 to a cavity 8 formed on the rear surface 7 of the head body 6, the back member 9 is heated to a high temperature. The temperature is set at about 750 degrees centigrade, approximated to standard finishing forging temperature if the member 9 is made of titanium or titanium alloy. As the back member 9 is fitted through deformation processing with the same being heated to the high temperature, the flow stress of the metallic material of the back member 9 can be lowered, thus enhancing ductility thereof. As a result, a front surface 14 and a peripheral surface 15 can be closely contacted by the cavity 8 without gaps, so that the back member 9 can be rigidly secured to the cavity 8. Thus the strength of the head is improved to enable the thickness of the face 4 to be made thinner.
Krumme et al., U.S. Pat. No. 6,277,033 describes a striking face for golf clubs, such as a driver, iron or putter, including zones of the same or different material arranged to create a desired xe2x80x9cfeelxe2x80x9d to the golfer and/or produce a desired effect on the golf ball. For instance, the zones can be arranged to create a variation in mechanical properties across the striking face. The zones can be created by using xe2x80x9cpixelsxe2x80x9d such as round or hexagonal rods arranged with their central axes perpendicular to the striking face. Pixels of a first material such as a shape memory alloy such as superelastic NiTi can be arranged in one or more concentric patterns and the remainder of the striking face can be made up of pixels of a second material such as beta-titanium, martensitic NiTi or stainless steel. The superelastic NiTi pixels can thus create a sweet spot on the striking face of the club.
Kosmatka, U.S. Pat. No. 6,299,547 describes a golf club having a club head with a thin, flexible striking plate for improved energy transfer to a golf ball also has a means for limiting the deflection of the striking plate during high speed impacts with the golf ball. A brace is positioned within the interior of the golf club head a predetermined distance from the striking plate to limit the deflection of the thin, flexible striking plate.
Hancock, 9-103523 describes a method to manufacture metal wood golf club heads that includes formation of a one piece main body consisting of a hosel, sole and club face, formation of the top, and fixation of the top to the main body. The main body and the top part of the club is formed by forging or cold pressing metals, particularly by forging or cold pressing titanium or its alloys, aluminum or its alloys, or aluminum alloy 7075, in particular.
The prior art teaches the use of forging titanium alloys and other metals for producing metal wood club faces, but does not teach a forging method for producing the very thin and super-strong metal faces defined in the present invention. The prior art also fails to teach a face that includes a crown portion or a crown and sole portion for improved durability of the part over long use. The present invention fulfills these needs and provides further related advantages as described in the following summary.
In the past 10 to 15 years the use of titanium alloys for golf club woods provides basic advantages over other high strength materials, such as stronger, lighter, superior sound, and excellent vibration damping. The wood driver produced in titanium gives the highest strength to weight ratio for further upsizing of head, resulting in increased moment of inertia, larger carry, excellent directionality, longer yardage and larger sweet spot.
The hitting faces produced by forging or forming processes have become increasingly popular over the past five years with the improved flexibility in face materials and design. It is known that basic characteristics of hitting faces often play a major role in the performance and quality of golf club heads, however, no attempt have been made to address the forge-processing with precise metallurgical control to produce the hitting faces with net or near-net shapes, along with grain flow control and refinement. This type of face achieves a higher degree of directional strength, impact strength and toughness, reduced face thickness, superior sound and excellent vibration damping, and a greater coefficient of restitution. The thickness of club faces with a macro-fiber lamella structure can be reduced to as low as 0.055 inches to achieve greater coefficient of restitution, ranging from above 0.80 to as high as 0.88 under test conditions such as specified by the United States Golf Association. The inventive process combines low cost with improved control of grain flow orientation.
In recent years, the application of xcex2-Ti alloys have further enhanced the hitting face properties with excellent strength, toughness, and modulus combinations. It offers superior properties in higher strength and good xe2x80x9chitxe2x80x9d feel, as well as an increased degree of design freedom especially when using Ti-6Al-4V, an xcex1+xcex2 titanium alloy. From a metallurgical consideration, it is known that fiber processing of alloys along metal flow orientation by large forge-deformation offers a product with structural integrity, greater metallurgical soundness and improved mechanical properties. The process deliberately orients the grains in directions requiring maximum strength and other properties, similar to lamella structures or metal-matrix composite. This produces directional alignment or grain flow for increased directional properties in strength, ductility and resistance to impact and fatigue. However, the process requires a combination of closely controlling metallurgical, processing, operational and design variables.
The following discusses various routes that may be taken in hot die forging to achieve, net, or near net shapes in titanium alloys. Near net refers to the production of a part that requires little, if any further finishing operations. Therefore, it is ready for use directly from the forge.
There are three commercial processing routes commonly used for the manufacture of titanium forgings and each has its merits and weaknesses related to resultant structure and properties. The first is the xe2x80x9calpha+beta prefinish with alpha+beta finish,xe2x80x9d which is the conventional processing route generally used to provide globular-primary alpha microstructure of the forgings for good strength, ductility, and low cycle fatigue capability. The second type is the xe2x80x9cbeta prefinish with beta finishxe2x80x9d forge processing, particularly designed to improve alloy processability and to improve fracture toughness, controlled creep property and crack growth resistance, resulting from an elongated Widmanstatten or colony alpha structure. The third process is the xe2x80x9cbeta-prefinish with alpha+beta finishxe2x80x9d processing route, which is used to improve ductility and LCF properties from beta-forged components, it balances the properties by producing a mixed equiaxed-elongated alpha structure.
Constrained avenues of thermomechanical processing are generally necessary to achieve the desired balance of strength, toughness, and ductility for producing titanium alloy forgings especially at high strength. The resultant beta-grain size and morphology, the degree of alpha+beta deformation in the two-phase region, the alpha-phase morphology and density have close relationships with the resultant tensile strength, ductility and fracture toughness. From a metallurgical standpoint, by manipulating appropriate hot working above and/or below the beta-transus, the alloy is progressively recrystallized and/or strained to achieve the best end products. Forge processes of xcex2-preforms with extensive alpha+beta deformation may be utilized in order to create extended grain flow and to refine the microstructures to assure the desired properties throughout the forging. Hot-die/isothermal forging is a deformation process during which the forging dies are maintained at the same or a temperature slightly below that of the alloy being deformed. The manufacturing capability for the hot die forging has been commercially demonstrated over a wide range of aerospace structural and engine components for more than 25 years. This technology was developed by the present inventor and co-workers during the 1970""s. By hot die forging the influence of die-chilling and material strain hardening can be reduced or eliminated. Thus, alloy forgeability can be maximized and the forging structure and properties can be optimized.
Hot dies decrease the differential between the forging stock and die temperatures, allowing a more uniform flow and refined shape of the forged component to be produced in a given operation, the details of the temperature and the strain path throughout the entire cross section of the forging can be carefully established and controlled. As a result, more refined shape, better material utilization, reduced number of forging operations, and precise control of processing variables achieves a net- or near-net shape, without additional, expensive machining operations. The present invention teaches certain benefits in construction and use which give rise to the objectives described below.
The present invention provides a hitting face of a metal wood golf head produced by a precise metallurgically controlled process. The hitting face is produced by macro-fiber processing of xcex2-preforms to produce a net, or near net-shape titanium face. The hitting face produced by this control of grain flow and metal deformation provides products with excellent directional strength, impact strength and toughness. This hitting face will assemble to a one piece casting comprising a crown, a sole and a hosel to form a high performance metal wood driver.
A primary objective of the present invention is to provide a driver face and method of manufacture of such a face that provides advantages not taught by the prior art.
Another objective is to provide such a face capable of assembly to a driver head housing with little or no further machining or finishing steps.
A further objective is to provide such a face capable of superior control of thickness and with a net thickness below that achieved with prior art processes.
A still further objective is to provide such a face capable of a higher coefficient of restitution.
A still further objective is to provide such a face capable of a longer life and less likelihood of sudden failure.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.